Amphiphilic nanosheets and methods of making the same

ABSTRACT

In some embodiments, the present invention provides amphiphilic nanosheets that comprise lamellar crystals with at least two regions: a first hydrophilic region and a second hydrophobic region. In some embodiments, the amphiphilic nanosheets of the present invention also comprise a plurality of functional groups that are appended to the lamellar crystals. In some embodiments the functional groups are hydrophobic functional groups that are appended to the second region of the lamellar crystals. In some embodiments, the lamellar crystals comprise α-zirconium phosphates. Additional embodiments of the present invention pertain to methods of making the aforementioned amphiphilic nanosheets. Such methods generally comprise appending one or more functional groups to a stack of lamellar crystals; and exfoliating the stack of lamellar crystals for form the amphiphilic nanosheets.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 14/624,974, filed Feb. 18, 2015. U.S. patent application Ser.No. 14/624,974 is a continuation of U.S. patent application Ser. No.13/848,669 filed Mar. 21, 2013. U.S. patent application Ser. No.13/848,669 claims the benefit of the entire disclosure of U.S.Provisional Patent Application No. 61/613,668 filed Mar. 21, 2012. U.S.patent application Ser. No. 14/624,974, U.S. patent application Ser. No.13/848,669, and U.S. Provisional Patent Application No. 61/613,668 areincorporated herein by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

This invention was made with government support under Grant Nos.DMR-1006870 and DMR-0652166, both awarded by the National ScienceFoundation. The government has certain rights in the invention.

BACKGROUND OF THE INVENTION

Current surfactants have numerous limitations in terms of solubility,durability and effectiveness. Current methods of making surfactants alsohave limitations in terms of efficiency and mass production. Therefore,a need exists for the development of more effective surfactants andmethods of making them.

BRIEF SUMMARY OF THE INVENTION

In some embodiments, the present invention provides amphiphilicnanosheets that comprise lamellar crystals with at least two regions: afirst hydrophilic region, and a second hydrophobic region. In someembodiments, the amphiphilic nanosheets of the present invention alsocomprise a plurality of functional groups that are appended to thelamellar crystals. In some embodiments, the amphiphilic nanosheets havethicknesses ranging from about 0.5 nm to about 5 nm, and diametersranging from about 10 nm to about 10 μm.

In some embodiments, the functional groups include at least one of alkylgroups, aryl groups, amine groups, polyamine groups, amide groups, estergroups, epoxy groups, carbonyl groups, alcohol groups, urethanes,isocyanates, aminosilanes, and combinations thereof. In someembodiments, the functional groups are hydrophobic functional groupsthat are appended to the second region of the lamellar crystals.

In some embodiments, the lamellar crystals include at least one ofclays, zirconium phosphates, titanium phosphates, hafnium phosphates,silicon phosphates, germanium phosphates, tin (IV) phosphates, lead (IV)phosphates, niobates, titanates, organic crystals, graphites, graphenes,polyhydroxybutyric acids, and combinations thereof. In some embodiments,the lamellar crystals comprise α-zirconium phosphates.

Additional embodiments of the present invention pertain to methods ofmaking the aforementioned amphiphilic nanosheets. Such methods generallycomprise appending one or more functional groups to a stack of lamellarcrystals and exfoliating the stack of lamellar crystals to form theamphiphilic nanosheets.

In some embodiments, the appending step includes the covalent linkage ofone or more functional groups to the stack of lamellar crystals. In morespecific embodiments, the appending step includes covalently linkinghydrophobic functional groups to the second region of the lamellarcrystals in order to make the region hydrophobic.

In some embodiments, the exfoliating step includes sonicating the stackof lamellar crystals. In some embodiments, the exfoliating step includesexposing the stack of lamellar crystals to an ionic composition, such astetra-(n-butylammonium) hydroxide.

The amphiphilic nanosheets of the present invention have numerousapplications. For instance, in some embodiments, the amphiphilicnanosheets can be used as surfactants in various settings.

BRIEF DESCRIPTION OF THE FIGURES

FIGS. 1A and 1B provide illustrations of a disk-shaped Janus particle(FIG. 1A) and its interfacial adsorption (FIG. 1B).

FIGS. 2A-2C show α-zirconium phosphate (α-ZrP) crystals. FIG. 2A is ascanning electron micrograph (SEM) image of the crystals. FIG. 2B is azoomed in view of the crystals showing cracks along the lamellar layers.FIG. 2C depicts structures of the alpha phase of the α-ZrPs.

FIG. 3 provides a two dimensional schematic representation of thefabrication of thin-surface and edge-modified amphiphilic nanosheets.The initial step consists of the grafting of a coupling agent over thesurface of the α-ZrPs. Subsequently, the exfoliation of the crystals iscarried out to obtain the surface and edge-modified nanosheets fromtheir outer and inner layers, respectively.

FIGS. 4A-4D shows transmission electron micrograph (TEM) images ofseveral non-modified α-ZrP nanosheets.

FIGS. 5A-5I summarize various properties of pristine α-zirconiumphosphate crystals. FIGS. 5A-4F show SEMs of different α-ZrP sizessynthesized via the hydrothermal method at 200° C. under differentconditions (phosphoric acid concentration−reaction time): (FIG. 5A) 9M-5hours, (FIG. 5B) 12M-5 hours, (FIG. 5C) 15M-5 hours, (FIG. 5D) 9M-24hours, (FIG. 5E) 12M-24 hours, and (FIG. 5F) 15M-24 hours. FIG. 5Gsummarizes the quantification of the diameter (gray bar) and thethickness (black bar) of the α-ZrP crystals. FIG. 5H shows an atomicforce microscope (AFM) contact mode topography image of a pristine α-ZrPcrystal fabricated using 9M phosphoric acid for 24 hours over a Si(100)surface modified with 3-aminopropyl trichlorosilane (APTES). FIG. 5Ishows section analysis for the cross-section white line seen in FIG. 5H,which gives a thickness of around 38 nm.

FIG. 6 provides a reaction mechanism for the grafting of octadecylisocyanate (ODI) to the edges and outer surfaces of α-ZrP crystals.

FIG. 7 shows Fourier transform infrared spectroscopy (FTIR) of anα-Zirconium phosphate surface with grafted ODI groups. Graph 1 showsα-ZrP. Graph 2 shows ODI. Graph 3 shows the grafted product.

FIGS. 8A-8C show X-ray photoelectron spectroscopy (XPS) andthermogravimetric analysis (TGA) spectra of the product obtained fromthe reaction of ODI with α-ZrP. FIG. 8A shows that the de-convolution ofthe C1s spectrum exhibits three peaks, consistent with the presence ofthe N—C(═O)— and carbon atoms. FIG. 8B shows the N1s spectra. FIG. 8Cshows the thermal stability of pristine α-ZrP (blue line) and α-ZrPgrafted with ODI (green line) analyzed by TGA.

FIGS. 9A-9C show atomic force microscopy (AFM) contact mode topographyimage and section analysis of an amphiphilic α-ZrP-ODI nanosheet over aSi(100) surface modified with octadecyltrichlorosilane (OTS). FIGS. 9Aand 9B show 2D and 3D topography images, respectively. FIG. 9C shows asection analysis, which indicates a thickness of around 2.8 nm (0.63 nmof a α-ZrP monolayer and 2.17 nm of the aliphatic chain) for thecross-section white line seen in FIG. 9A.

FIGS. 10A-10I provides data related to the characterization of stableemulsions stabilized by α-ZrP-ODI nanosheets and unstable emulsionsusing non-modified α-ZrP nanosheets. Representative (FIG. 10A) opticalmicrograph and (FIG. 10B) confocal laser scanning micrograph ofoil-water (o/w) emulsions using α-ZrP-ODI as surface-active agents areshown. In addition, FIG. 10C provides observation of o/w emulsionsstabilized by non-modified α-ZrP monolayers. The emulsion coalesced andquickly creamed. FIG. 10D shows optical micrographs of the o/w emulsionright after emulsification and (FIG. 10E) after 24 days, which indicatesthat non-modified α-ZrP nanosheets are not good emulsifiers due to theobserved coalescence. FIG. 10F shows the creaming of o/w emulsionsstabilized by α-ZrP-ODI nanosheets. The emulsion presents less creamingcompared to FIG. 10C due to the less degree of coalescence. FIG. 10G isa micrograph showing the oil-in-water droplets after emulsifying. FIG.10H is an o/w emulsion micrograph from the top and (FIG. 10I) from themiddle after 24 days, where no coalescence was observed. Pictures of(FIGS. 10A, 10D-E, and 10G-I) were taken using a Nikon microscopeTE-2000U with 20× magnification. FIG. 10B was taken using a Leicaconfocal microscope TCS SP5 with magnification of 100×. Digitalphotographs shown in FIGS. 10C and 10F were taken using a Sony DSC-220Wdigital still camera.

FIGS. 11A and 11B show various data related to toluene-in-wateremulsions. FIG. 11A shows toluene-in-water emulsion droplet diameter asa function of α-ZrP-ODI nanosheet concentration after one week. Thetoluene volume fraction is ϕ_(o)=0.085. FIG. 11B shows droplet diameterof toluene-in-water emulsions as a function of time. The concentrationof α-ZrP-ODI nanosheets is 0.45 wt. %.

FIGS. 12A-12C show toluene-in-water emulsions stabilized by α-ZrP-ODIand non-modified α-ZrP nanosheets where toluene concentration wasϕ_(o)=0.12. FIG. 12A shows a micrograph of uniform toluene-in-waterdroplets stabilized by α-ZrP-ODI nanosheets. The diameter of thedroplets is 3.05±0.42 μm. FIG. 12B shows a micrograph of polydispersedtoluene-in-water emulsion droplets stabilized by non-modified α-ZrPnanosheets. FIG. 12C shows toluene-in-water emulsions stabilized bynon-modified α-ZrP (right) showing strong creaming due to large dropsize and stabilized by α-ZrP-ODI nanosheets (left) with a less creamingeffect. The picture is taken at 200 hours after emulsification.

FIG. 13 shows data related to Pickering miniemulsion polymerization ofstyrene using α-ZrP-ODI nanosheets as stabilizers. Average polystyreneparticle diameter is plotted as a function of weight percent ofplatelets.

FIGS. 14A-14D show images of Pickering miniemulsions ofstyrene-in-water. FIG. 14A is an SEM image ofplatelet-armored-polystyrene particles. FIGS. 14B-D are TEM images ofplatelet-armored polystyrene particles.

FIG. 15 is plot of the concentration of amphiphilic nanosheets on thesurface of polystyrene particle surfaces (C_(surface)) as a function oftotal concentration of platelets (C_(o)).

FIGS. 16A-16D show contact angle measurements for seven differentsamples at different α-ZrP-ODI nanosheet concentrations.

FIG. 17 shows idealized structures for octadecyl isocyanate, tetradecylisocyanate, octyl isocyanate, and pentyl isocyanate. These compoundswere used to graft the edge and the outer surfaces of α-ZrP crystals of161 nm (RF, 12M-24 hours, 100° C.).

FIG. 18 shows idealized structures of the linear and branched isocyanatehydrocarbons; linear n-butyl isocyanate and branched sec-butylisocyanate and tert-butyl isocyanate.

FIG. 19 shows solid state MAS NMR of acetone-2-¹³C sorbed on zirconiumbiphenylenebis(sulfophosphonate), in which the surface is saturated byacetone

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory only,and are not restrictive of the invention, as claimed. In thisapplication, the use of the singular includes the plural, the word “a”or “an” means “at least one”, and the use of “or” means “and/or”, unlessspecifically stated otherwise. Furthermore, the use of the term“including”, as well as other forms, such as “includes” and “included”,is not limiting. Also, terms such as “element” or “component” encompassboth elements or components comprising one unit and elements orcomponents that comprise more than one unit unless specifically statedotherwise.

The section headings used herein are for organizational purposes onlyand are not to be construed as limiting the subject matter described.All documents, or portions of documents, cited in this application,including, but not limited to, patents, patent applications, articles,books, and treatises, are hereby expressly incorporated herein byreference in their entirety for any purpose. In the event that one ormore of the incorporated literature and similar materials defines a termin a manner that contradicts the definition of that term in thisapplication, this application controls.

Amphiphilic particles are both hydrophilic and hydrophobic. Acting assurfactants, they are able to stabilize liquid-liquid interfaces to formPickering emulsions (emulsions stabilized by particles). Two types ofamphiphilic particles are the Janus particles and Gemini particles.Janus particles generally have two hemispheres or halves withdistinguishable differences in chemical properties. Currently, there areseveral methods to prepare Janus particles. For example, Janus particlescan be obtained from double-emulsion droplets using microfluidics,electrohydrodynamic jetting of parallel polymer solutions, metalcoating, and a hierarchical self-assembly process. Janus particles arealso building blocks for supra-particular assemblies based on theiranisotropy, which offers a gamut of other applications, such as drugdelivery agents, photonic crystals, electronics, and photolithography.Janus particles are strongly adsorbed to interfaces, where they act assurfactants for the formation of stable Pickering emulsions.

Gemini molecular surfactants can be described as molecules having a longhydrocarbon sequence, followed by a charged group (cationic, anionic, ornonionic), a spacer (rigid or flexible), a second charged group, andanother hydrocarbon chain segment. Regular surfactants are characterizedby their critical micelle concentrations (CMCs), above which themolecules prefer to join the micelle rather than the interface. Geminimolecules are well known to possess lower CMC values than do thesurfactants of equivalent chain length, making them more efficient inlowering surface tension.

Although Janus particles function as regular surfactants in terms oftheir function in stabilizing Pickering emulsions (as the counterpart tothe Gemini surfactants), the Gemini particles have not yet beenfabricated. Furthermore, there is a need to create more effectiveviscoelastic surfactants that combine viscosity with surfactancy. Thepresent invention addresses these needs by demonstrating the fabricationof surface and edge-modified amphiphilic nanosheets by the use oflamellar crystals.

As set forth in more detail below, the methods and compositions of thepresent invention have numerous variations. More specific andnon-limiting embodiments of the present invention will now be describedin more detail.

Amphiphilic Nanosheets

In some embodiments, the present invention pertains to amphiphilicnanosheets. Such nanosheets generally include lamellar crystals with atleast two regions: a first hydrophilic region and a second hydrophobicregion. In some embodiments, the amphiphilic nanosheets of the presentinvention also include one or more functional groups that are appendedto the lamellar crystals.

As set forth in more detail below, various lamellar crystals may beutilized in the amphiphilic nanosheets of the present invention.Likewise, various functional groups may be appended to various regionsof the lamellar crystals.

Lamellar Crystals

Lamellar crystals generally refer to polycrystalline compositions thatare in the form of thin sheets (e.g., sheets with thicknesses rangingfrom about 0.5 nm to about 5 nm). The amphiphilic nanosheets of thepresent invention may include various lamellar crystals. In someembodiments, the lamellar crystals include, without limitation, clays,zirconium phosphates (α-ZrP), titanium phosphates (α-TIP), hafniumphosphates (α-HfP), silicon phosphates (α-SiP), germanium phosphates(α-GeP), tin (IV) phosphates (α-SnP), lead (IV) phosphates (α-PbP),niobates, titanates, organic crystals, graphites, graphenes,polyhydroxybutyric acids, and combinations thereof.

In more general embodiments, the lamellar crystals of the presentinvention include crystals of atoms from columns IVB, VIA, and VA of theperiodic table of elements. In some embodiments, such atoms may also beassociated with P, O and H.

In various embodiments, the lamellar crystals of the present inventioncan stack into layered compounds and be exfoliated into layers. In someembodiments, the lamellar crystals of the present invention can havevarious regions with different properties. For instance, in someembodiments, the lamellar crystals of the present invention may have oneregion that is hydrophilic and another region that is hydrophobic. Insome embodiments, such regions may be surfaces, edges, or combinationsof surfaces and edges. For instance, in more specific embodiments, thelamellar crystals may have one surface that is hydrophilic and anotheropposite surface that is hydrophobic.

In various embodiments, different functional groups may be appended todifferent regions of the lamellar crystals in order to confer thedifferent properties.

Functional Groups

Various regions of the lamellar crystals of the present invention may befunctionalized with various functional groups. Such functional groupsmay include, without limitation, cationic functional groups, anionicfunctional groups, nonionic functional groups, and combinations thereof.In some embodiments, the functional groups are monomeric molecules. Insome embodiments, the functional groups are polymers. In variousembodiments, the lamellar crystals may be covalently or non-covalentlyfunctionalized with such functional groups.

Non-limiting examples of functional groups that may be appended tolamellar crystals may include, without limitation, alkyl groups, arylgroups, amine groups, amide groups, ester groups, epoxy groups, carbonylgroups, alcohol groups, urethanes, isocyanates, silanes, aminosilanes,and combinations thereof. In more specific embodiments, the functionalgroups include, without limitation, 3-aminopropyl trichlorosilane(APTES), octadecyl isocyanate, 3-(trethoxysilyl)propyl isocyanate,4-(trechlosilyl)butyronitrile, trichloro(phenyl)silane,3-(methacryloyloxy)propyl trimethoxysilane (MOPT),trans-1,4-cyclohexylene diisocyanate, 1,6-diisocyanatohexane, andcombinations thereof. In more specific embodiments, the functionalgroups include octadecyl isocyanate (ODI).

Functional groups may be appended to various regions of lamellarcrystals. In some embodiments, the functional groups may be appended toone or more surfaces or edges of the lamellar crystals. Furthermore,different regions of lamellar crystals may have functional groups withdifferent properties. For instance, in some embodiments, a surface of alamellar crystal may be functionalized with hydrophilic functionalgroups while another surface of the lamellar crystal may befunctionalized with hydrophobic functional groups. Such hydrophilic andhydrophobic functional groups can in turn confer hydrophilic andhydrophobic properties on the respective surfaces. In more specificembodiments, a surface or region of a lamellar crystal may befunctionalized with hydrophobic functional groups while other surfacesor regions remain unfunctionalized.

In some embodiments, the functional groups on the surfaces or edges oflamellar crystals can be further chemically reacted to extend and/orchange functions or properties. In various embodiments, each surface,edge or region of lamellar crystals may also have multiple functionalgroups with different properties. In more specific embodiments, thelamellar crystals may have functional groups on surfaces, edges orregions that have a long hydrocarbon sequence, followed by a chargedgroup (cationic, anionic, or nonionic), a spacer (rigid or flexible), asecond charged group, and another hydrocarbon chain segment. Forlamellar crystals that form Janus platelets, top and bottom surfaces ofthe plates may be functionalized with chemically different functionalgroups (e.g., hydrophilic and hydrophobic functional groups) in someembodiments. For lamellar crystals that form Gemini platelets, thefunctional groups may be attached to the edges.

Properties

The formed amphiphilic nanosheets of the present invention can also havevarious properties and arrangements. For instance, the amphiphilicnanosheets can have various sizes, widths, thicknesses, andcrystallinities. Furthermore, the size distribution can be monodisperseor polydisperse.

In some embodiments, the amphiphilic nanosheets of the present inventionmay have thicknesses that range from about 0.5 nm to about 5 nm. In morespecific embodiments, the amphiphilic nanosheets of the presentinvention may have thicknesses that range from about 0.5 nm to about 5nm. In further embodiments, the amphiphilic nanosheets of the presentinvention have a thickness of about 2.2 nm.

In some embodiments, the amphiphilic nanosheets of the present inventionmay have diameters that range from about 10 nm to about 10 μm. In morespecific embodiments, the amphiphilic nanosheets of the presentinvention have a diameter of about 1 μm. In more specific embodiments,the amphiphilic nanosheets of the present invention may have diametersof about 20 nm and thicknesses of about 2-3 nm. In further embodiments,such amphiphilic nanosheets may include α-ZrP crystals.

The amphiphilic nanosheets of the present invention may also havevarious surface areas. For instance, in some embodiments, theamphiphilic nanosheets of the present invention (such as α-ZrPnanosheets) may have surface areas that range from about 1 m²g⁻¹ toabout 200 m²g⁻¹.

The amphiphilic nanosheets of the present invention may also havevarious aspect ratios. For instance, in some embodiments, theamphiphilic nanosheets of the present invention (such as α-ZrPnanosheets) may have aspect ratios that range from about 3500 to about10.

The amphiphilic nanosheets of the present invention may also be capableof self-assembly. Furthermore, the amphiphilic nanosheets of the presentinvention may have various arrangements. For instance, in someembodiments, the amphiphilic nanosheets of the present invention may bearranged as stacks of nanosheets, individual sheets, or combinationsthereof.

As also set forth previously, the amphiphilic nanosheets of the presentinvention can have different regions with different properties (e.g.,edges or surfaces with hydrophobic and/or hydrophilic properties). Asset forth in more detail below, such different properties providenumerous advantages.

Methods of Making Amphiphilic Nanosheets

Additional embodiments of the present invention pertain to methods ofmaking the amphiphilic nanosheets of the present invention. In someembodiments that are depicted in FIG. 3, the method comprises: (1)appending one or more functional groups to a stack of lamellar crystals;and (2) exfoliating the stack of lamellar crystals to form theamphiphilic nanosheets. In some embodiments, the formed nanosheetscomprise at least two regions: a first hydrophilic region and a secondhydrophobic region. As set forth below, various methods may be used toappend functional groups to lamellar stacks and exfoliate the lamellarcrystals.

Appending Functional Groups

Various methods may be utilized to append functional groups to lamellarcrystals. In some embodiments, the appending includes the covalentlinkage of one or more functional groups to the lamellar crystals. Inmore specific embodiments, the appending includes the covalent linkageof functional groups to one or more edges of the lamellar crystals. Infurther embodiments, the appending may include the covalent linkage offunctional groups to one or more surfaces of the lamellar crystals.

In some embodiments, the lamellar crystals are in stacked form duringfunctionalization. See, e.g. FIG. 3. In such embodiments, thefunctionalization may be site specific towards a surface or an edge.Thus, in some embodiments, such methods may be used to developsite-specific chemical reactions to functionalize the surfaces oflamellar crystals to be hydrophilic on one side (e.g., with hydrophilicfunctional groups, such as HPO₄ or no functional groups) and hydrophobicon the other side (e.g., with hydrophobic functional groups, such asphenyl groups).

In addition, various moieties and functional groups on lamellar crystalsmay be utilized for functionalization. For instance, as depicted in FIG.3, OH groups on the surface of lamellar crystals can be readily used tocarry out the chemical reactions. Furthermore, in various embodiments,some of the OH groups may be selectively protected and used later forlabeling or other needs. Hence, complex structures can be fabricated onthe lamellar crystals.

Exfoliating Lamellar Crystals

In cases where stacked lamellar crystals are functionalized, variousmethods may also be used to exfoliate the stacked and functionalizedlamellar crystals into individual sheets. In some embodiments, theexfoliating includes sonicating the stack of lamellar crystals. In someembodiments, the exfoliating includes exposing the stack of lamellarcrystals to an ionic composition, such as tetra-(n-butylammonium)hydroxide (TBA⁺OH⁻). In some embodiments, exfoliation may involve bothsonication and exposure to ionic compositions.

The aforementioned methods may also have numerous variations. Forinstance, in some embodiments, a subsequent functionalization step (aspreviously described) may also be carried out after an exfoliation step.In further embodiments, the cycle of functionalization and exfoliationmay be repeated numerous times with different functional groups to formstaged materials, where the surfaces of the lamellar crystals in eachlayer may be individually functionalized with the same or differentfunctional groups. Thus, in various embodiments, lamellar crystals withdifferent functional groups on each layer may be formed. For instance,in some embodiments, lamellar crystals with a hydrophobic layer (withphenyl groups) and a hydrophilic layer (with HPO₄ groups) may be formed.The hydrophobic group may then be functionalized, and the hydrophilicgroup exfoliated.

The methods of the present invention also provide high yield rates forthe production of amphiphilic nanosheets, which can be close to 100%theoretically. Such methods can also be used to mass produce amphiphilicnanosheets.

Advantages and Applications

The aforementioned methods of making amphiphilic nanosheets providenumerous advantages. In particular, the methods of the present inventionprovide a facile and continuous method of making bulk quantities ofJanus and Gemini particles. Previous methods of producing such particlesinvolved multiple steps, the use of protecting agents to protect half ofthe spheres first, and the need to get rid of the agents later.

The amphiphilic nanosheets of the present invention also providenumerous advantages. By way of background, there are opposite effects inthe stabilization of Pickering emulsions (emulsions stabilized byparticles) using spherical particles. For instance, stabilizationrequires particles as small as possible. However, smaller particles areeasy to escape the interface due to Brownian motion since the adsorptionenergy to the oil-water interface is proportional to the diameter of thespheres. In fact, it has been found that anisotropic particles with highaspect ratios are better emulsion stabilizers.

As set forth in more detail in the Examples below, the amphiphilicnanosheets of the present invention (such as α-zirconium phosphateplatelets) have established a platform for flexible design ofmultifunctional surfactants tailored for optimal performance. Inparticular, the highly anisotropic and amphiphilic nanosheets of thepresent invention reconcile the aforementioned opposite effects due tothe existence of length scales, thicknesses, and lateral size (2R_(d)).

The large aspect ratios of the amphiphilic nanosheets also offer optimalstability to the nanosheets between two emulsions to preventcoalescence. Likewise, the nanosheet's large lateral surface area offersstrong adsorption energy at the oil-water interface.

Thus, the amphiphilic nanosheets of the present invention providenumerous applications. For instance, the nanosheets can be used assurfactants, paints, cosmetic products, pharmaceutical products,detergents, emulsions, foam stabilizers, rheological thickeners fordrilling fluids, and coating agents. In more specific embodiments, theamphiphilic nanosheets of the present invention can be used to enhancethe stability of high expansion foam. In various embodiments, such foamsmay be used for fire extinguishing of liquefied natural gas (LNG). Insome embodiments, the amphiphilic nanosheets may be combined withcatalysts on one or more surfaces. This may in turn increase the load ofcatalysts in a particular region, such as reactors.

In further embodiments, the amphiphilic nanosheets of the presentinvention can be used for coating or cleaning solar cells. Theamphiphilic nanosheets of the present invention can also be used todeliver drugs, genes, and other compounds to a desired site in anorganism (e.g., a human patient). In addition, the amphiphilicnanosheets of the present invention can be used to make luminescent,conductive or semi conductive materials. The amphiphilic nanosheets ofthe present invention can also be used as alignment agents forbiomolecules in magnetic fields using NMR to measure the structure ofthe biomolecules. Furthermore, the amphiphilic nanosheets can be used tostabilize gas bubbles. Likewise, the amphiphilic nanosheets can be usedas contrast agents for ultrasound wave or cosmic waves.

The amphiphilic nanosheets of the present invention can also be used assmart devices. In particular, the grafting of pH- andtemperature-sensitive polymers to the nanosheets of the presentinvention can produce amphiphilic nanosheets suitable for drug deliveryand sensor applications. Such amphiphilic nanosheets can be responsiveto various environmental conditions, such as temperature fluctuations,changes in pH, and changes in salt concentrations.

In more specific embodiments, the amphiphilic nanosheets of the presentinvention can be used as surfactants to stabilize various emulsions,such as Pickering emulsions. In further embodiments, the amphiphilicnanosheets of the present invention can be used as surfactants forenhanced oil recovery, such as emulsifiers in microfluidic channels andreservoir rocks (e.g., porous rocks).

The amphiphilic nanosheets of the present invention could also be usedto stabilize contrast agents for ultrasonic imaging of colloids, such asgas bubbles. Two-dimensional amphiphiles could be also fabricated bygrafting coupling agents over the surface of other materials, such asgraphene or TiO₂ nanosheets.

Additional Embodiments

Reference will now be made to more specific embodiments of the presentdisclosure and experimental results that provide support for suchembodiments. However, Applicants note that the disclosure below is forexemplary purposes only and is not intended to limit the scope of theclaimed invention in any way.

The Examples below pertain to Pickering emulsions stabilized byamphiphilic nanosheets. In particular, in the Examples below, Applicantsdemonstrate the fabrication of amphiphilic nanosheets, which are eithersurface- or edge-modified plates with atomic scale thicknesses, thethinnest amphiphilic particles reported so far. The nanosheets areobtained by exfoliation of functionalized layered crystals, the firsttime that laminar structures have been utilized to produce suchparticles. Stable emulsions were made utilizing these nanosheets. Theadsorption of the amphiphilic nanosheets to the oil-in-water interfacesand the reduction of surface tension between the PDMS and theamphiphilic nanosheet suspensions were quantitatively characterized.

Pickering emulsions are emulsions stabilized by colloidal particles.Water-in-oil Pickering emulsions, formed using solid particles such asasphaltenes, are commonly the reason for the high stability of waterdroplets in crude oil. As solid particles are adsorbed onto thewater-oil interface, the surface energy of the system is reduced and,consequently, the emulsion is established. The stability of Pickeringemulsions depends on the size, shape, and wettability of particles atthe interface. Based on theory, spherical, acicular, and discoticparticles can be used as Pickering stabilizers to produce colloidosomes.Colloidosomes are microcapsules having a coagulated colloidal particleshell that can result from Pickering emulsions, as first synthesized byVelev. For example, platelet-like laponite clay has been used to preparelatex via Pickering miniemulsion polymerization.

Using homogeneous spheres, the highest stability of the resultingPickering emulsion occurs when the three-phase contact angle among theparticle, hydrophobic, and hydrophilic fluids is around 90°. Hydrophobicparticles will stabilize water-in-oil emulsions having a contact angleslightly greater than 90°, whereas hydrophilic particles will stabilizeoil-in-water emulsions having a contact angle slightly less than 90°. Inthe case of Janus spheres, the stability is measured using the energyrequired to remove a particle from equilibrium into the hydrophobicfluid and normalized by the energy of removing it from the hydrophilicfluid, which is the so called Janus balance J, J=(sin²α+2 cos θ_(p)(cosα−1))/(sin²α+2 cos θ_(a)(cos α+1)), where α is the angle from the centerof the sphere to the hydrophilic-hydrophobic boundary, θ_(p) is thecontact angle of the hydrophilic side, and θ_(a) is the contact angle ofthe hydrophobic side. The highest stability of the Pickering emulsionstabilized by Janus particles is achieved when J=1, which can beobtained via tuning the parameter a.

However, two opposite effects are at work in the stabilization ofPickering emulsions using spherical particles, which have only onelength scale, the diameter of the spheres 2r. First, the interfaces oftwo adjacent emulsions will endure a maximum capillary pressure rightbefore coalescence (P_(c) ^(max)), which can be expressed as P_(c)^(max)=±p(2γ_(ow)/r)(cos θ±z), where p is a theoretical parameter usedto link the influence of particle concentration (with a “+” signreferring to oil-in-water (o/w) emulsions and with a “−” sign referringto water-in-oil (w/o) emulsions), and z is a constant dependent upon onthe arrangement of particles in the interface. γ_(ow) is the interfacialenergy between the oil and the water, θ is the three-phase contact angleat the interface and r is the radius of the spheres. Hence, the smallerthe size of the spheres, the larger P_(c) ^(max) can be. Spheres with asmaller radius r, therefore, prevent emulsion coalescence better than dolarger spheres. Secondly, in the opposite effect, it is well known thatsmall particles tend to escape from the interface by thermalfluctuations. The free energy to remove a sphere from the interface isdefined by ΔG_(remove)=πτ²γ_(ow)(1+cos θ)². Therefore, spheres with asmaller radius r escape more easily from the interface by thermalfluctuation than do the larger spheres.

The highly anisotropic particles that Applicants used here couldreconcile these two effects due to the existence of two length scales,thickness h and lateral size 2R_(d). A nanosheet in the interface isequivalent to a closed packing of spheres filling the interstitialspace, where 2r_(s) (diameter of each sphere) corresponds to thethickness of the nanosheet thickness h. Also, the total area covered bythese spheres is equal to the area covered by the nanosheet. Theinterfaces of two adjacent emulsions will endure a maximum capillarypressure right before coalescence as P_(c) ^(max)≈±p(2 γ_(ow)/r_(s))(cosθ±z)≈±p(4γ_(ow)/h)(cos θ±z). The nanosheet thickness h can serve as aproxy for sphere diameter in the role of preventing emulsioncoalescence. The extremely small value of h offers a good capability tostabilize emulsions. Simultaneously, the nanosheets' large lateral size2R_(d) offers strong adsorption towards the interface, preventing itsescape due to thermal motion. The energy necessary to remove adisk-shaped Janus particle from its equilibrium position at theoil-water interface along the boundary between the hydrophobic andhydrophilic hemispheres is defined by ΔG_(min)=πR₂²(γ_(oP1)+γ_(wP2)−γ_(ow))+2πR_(d)(h₁γ_(oP1)+h₂γ_(wP2)), where πR_(d) ²is the cross-sectional area of the particle, h₁ and h₂ are thickness ofthe hydrophobic and the hydrophilic regions, respectively, and the sumof them is equal to the thickness of the disk. P₁ indicates thehydrophobic region and P₂, the hydrophilic region. γ_(oP1) and γ_(wP2)are the interfacial energies between the hydrophobic or hydrophilicregions and the oil or water interfaces, respectively. See FIGS. 1A-1B.FIG. 1 shows the case of oil in water emulsions. The same can berealized using the amphiphilic nanosheets to make water in oil emulsionsand complex emulsions, such as double emulsions (oil-in-water-in-oil;and water-in-oil-in-water).

A similar behavior is presented for spherical Janus particles. Thus,particles with a large cross-sectional area, πR_(d) ², can be stronglyadsorbed to the interface. Since ΔG_(remove)˜R_(d) ² and p_(c)^(max)−1/h, anisotropic particles with high aspect ratio (ξ=2R_(d)/h)can be good emulsion stabilizers. In the past, Lagaly et al. confirmedthat large-aspect-ratio plate-shaped clay particles together withnonionic surfactants could be used as stabilizers for emulsions bycreating a mechanical barrier to prevent coalescence. Additionally,surfactant-free o/w emulsions can be stabilized by synthetic clay(laponites), and, in this case, phase inversion was studied. Here,Applicants report amphiphilic nanosheets that are thin and have largeaspect ratios.

Lamellar crystals are characterized by their layered structure. They canbe inorganic crystals, such as clay, α-zirconium phosphates (α-ZrP) (asshown in FIGS. 2A-2C), niobates, titanates, or organic crystals, such asgraphite, which is formed by stacks of graphene layers. Lamellarcrystals often exhibit the morphology of nanosheets. See FIG. 2A. Theyare used as rheological thickeners for drilling fluids, paint,cosmetics, and pharmaceutical products. They have also been extensivelyinvestigated in polymer-clay nano-composites and electronics over pastdecades. They are distinguished by strong bonds in the x and ydirections in the plane of the flat crystal, but weaker interactionsbetween the layers in the direction. Lamellar crystals can, therefore,go through intercalation and exfoliation by guest molecules. Wheninteractions between the intercalated guest molecules are weak enough inthe interlayer region, an exfoliation, or separation of layers can takeplace. Among the most widely used lamellar crystals are the α phase ofzirconium phosphate (α-ZrP) with chemical formulas Zr(HPO₄)₂H₂O. SeeFIGS. 2A-2C. The α-ZrP crystal layer is composed of a ZrO₆ sheetcoordinated with HPO₄ ²⁻ tetrahedrons forming a covalent network. SeeFIG. 2C. The thickness of a monolayer of α-ZrP is about 0.66 nm (0.63 nmif the phosphate groups are deprotonated).

Here, Applicants bridge these two thus far independently developingfields of amphiphilic particles and lamellar compounds, demonstratingthe ability to create thin amphiphilic nanosheets analogous to Janus(JPs) and Gemini (GPs) nano-plates, which are indeed just the thicknessof a single layer of O, P, and Zr atoms, via the functionalization oflamellar crystals followed by exfoliation. In fact, functionalizednanosheets belong to the general category of amphiphilic particles atthe “zero” size limit (atomic scale) in one dimension. Within theirparticle family, they are the closest to conventional surfactantmolecules. They are viewed best, however, as assembled clusters ofsurfactants organized laterally. The single nano-plate layer is rigidwhen the nanosheet size is about several tenths of a nanometer or lessand become flexible when the size is larger than a hundred nanometers,depending on the bending elasticity of the layer. The impermeable natureof the crystalline layer serves as a barrier, preventing diffusion ofsmall molecules, and, hence, the coalescence of emulsions “wrapped” byit.

Example 1. Grafting and Exfoliation of α-ZrP

α-ZrP is characterized by a strong hydrophilicity. Hence, chemicalmodification is required to convert it to become hydrophobic. First, acoupling agent is grafted over the exposed edges and flat surfaces ofthe α-ZrP crystals. See FIG. 3 (grafting step). Subsequently, via theexfoliation of these crystals, a mixture of thin-surface andedge-modified amphiphilic nanosheets are obtained from the outer and theinner layers, respectively. See FIG. 3 (exfoliation step) and FIGS.4A-4D (showing the transmission electron microscope (TEM) images of theα-ZrP nanosheets).

As shown in FIGS. 4A-4D, the α-ZrP nanosheets are thin and flexible, andcan present wrinkles, as shown in FIGS. 4B and 4C. This demonstratesthat the nanosheets can bend on the oil-water interface to stabilize theemulsions. It has been proven that the single nano-plate layer is rigidwhen the nanosheet size is about several tenths of a nanometer or lessand becomes flexible when the size is larger than a hundred nanometers,depending on the bending elasticity of the layer.

The resulting nano-plates are amphiphilic. Exfoliation of the lamellarcrystals occurs when enough tetra-(n-butylammonium) hydroxide (TBA⁺OH⁻)is added to exceed single-layer packing of TBA⁺ ions in the interlayerregion. The mono-layers obtained are atomically flat, mechanicallystrong, flexible and chemically stable in common basic and acidicsolvents. The α-ZrP crystals are easy to synthesize, and the crystalsize and size polydispersity are highly tunable by varying phosphoricacid concentration, reaction time, and reaction temperature. Inaddition, α-ZrP crystals are able to achieve complete exfoliation. SeeFIGS. 5A-5I.

It is well known that α-ZrP presents low reactive hydroxyl groups on itssurfaces. Although numerous studies have reported intercalation ofseveral compounds into α-ZrP, a direct grafting reaction on ZrP crystalsurfaces had not been evaluated consistently, and just a few studies canbe found in literature. The surface modification here consists of achemical (covalent) reaction of the OH groups on the surface of α-ZrPwith octadecyl isocyanate (ODI) as a coupling agent.

As illustrated in FIG. 6, the particles created in the current studywere synthesized by grafting ODI over the edges and the outer surfacesof α-ZrP crystals. The intercalation of the ODI into α-ZrP does not takeplace due to the high hydrophobicity of the ODI and the highhydrophilicity of the interlayer region. The ODI coupling agent is oneof the most broadly used functional group reagents in synthesisreactions due to the high reactivity of its functional group, —NCO. Ithas been reported that the isocyanate group reacts with the hydroxylgroups of the hydroxyapatite (Ca₅(PO₄)₃OH) crystals. In fact, thereactivity of the hydroxyapatite surface hydroxyl groups towards theorganic isocyanate groups has been confirmed. In addition, previous workalso reported the grafting of different organic silane coupling agentson the surface of the calcium phosphate through the reaction with itssurface hydroxyl groups.

Example 2. Synthesis and Functionalization of α-ZrPs

The synthesis of the highly crystalline α-ZrP by the hydrothermal methodhas been described by Sun et al. Sun, L. Y.; Boo, W. J.; Sue, H. J.;Clearfield, A. New J. Chem. 2007, 31, 39. Particularly, 6 g ZrOCl₂.8H₂Owere mixed with 60 mL (9 M) H₃PO₄ and heated at 200° C. for 24 hours ina high-pressure autoclave. After the reaction, the product wascentrifuged and washed three times with deionized (DI) H₂O and driedovernight at 60° C. The dried product was ground with a mortar andpestle into a fine powder. Highly crystalline α-ZrP was used to avoidthe intercalation of the modifier in the surface and edge modificationstep. Finally, the crystals were reacted with octadecyl isocyanate(Aldrich, 98%) in a 1:10 (ODI:ZrP) molar ratio at 65° C., using o-xyleneas a solvent, for 12 hours under nitrogen. The resulting product waswashed with methanol three times and dried at 60° C. overnight in anoven.

Example 3. Characterization of the Modified α-ZrPs

The resulting powder was characterized by Fourier transform infrared(FTIR, Shimadzu IRAffinity-1 spectrometer in an ATR, attenuated totalreflection mode with a ZnSe ATR Prism Model Pike MIRacle A, Columbia,Md.) and thermogravimetric analysis (TGA, Q500 TA Instrument, NewCastle, Del.). AFM images were collected with an Agilent/MolecularImaging PicoSPM coupled with an RHK Technology SPM 1000 ElectronicsRevision 8, and X-ray photoelectron spectroscopy (XPS, Kratos Axis UltraImaging, Chestnut Ridge, N.Y.) to analyze the elementary composition ofthe final compound.

Fourier Transform Infrared Spectroscopy (FTIR)

The grafting reactions (i.e., the outer surface modification reactions)were analyzed by Fourier transform infrared spectroscopy (FTIR). SeeFIG. 7. The FTIR spectrum of pristine α-ZrP is shown in Graph 1 of FIG.7. Applicants observed that the isocyanate band (—N═C═O) at 2260 cm⁻¹(shown in FIG. 7, Graph 2) vanished after reaction. In the meantime, anew band at 3375 cm⁻¹ appeared, which corresponds to a secondary amine(R′R—N—H). See FIG. 7, Graph 3. In addition, the CH₂ and CH₃ symmetricand asymmetric stretching bands at 3000-2850 cm⁻¹ were observed in theproduct.

FTIR spectra contained two C═O bands, at 1685 cm⁻¹ for the estercarbonyl (—RC(O)O—) and 1525 cm⁻¹ for amide II (—RR′C(O)NH), aspredicted in FIG. 6. The presence of amide bands and the disappearanceof the isocyanate band indicated that the hydroxyl groups over thesurface of α-ZrP reacted with the isocyanate groups and resulted in theformation of a urethane linkage. The sharp bands located at 3590 cm⁻¹and 3510 cm⁻¹ for pristine α-ZrP and the surface-modified product wereattributed to the asymmetric and symmetric stretching of theintercalated water, while the one located at 1620 cm⁻¹ was attributed tothe bending vibration of water. The remains of the intercalated water,after completion of the grafting reaction, indicated that nointercalation of the lamellar crystals occurred during the graftingreactions because of the high crystallinity of the pristine ZrPcrystals.

X-Ray Photoelectron Spectroscopy (XPS)

X-ray photoelectron spectroscopy (XPS) analysis was conducted using aKratos Axis Ultra Imaging XPS system to measure the film compositionthat complements the infrared analysis. The binding energy of carbon(C(1s):285 eV) was used as the reference for data calibration. XPS is ahighly diagnostic tool for the assessment of the chemical state of theelements. It has been used before to characterize α-ZrP and its organicderivatives. The XPS spectra of octadecyl isocyanate (ODI) grafted toα-ZrP is shown in FIGS. 8A-8C. The C(1s) peak located at E_(b)=287.7 eVcorresponds to the carbons in the aliphatic chain, and the peak locatedat 289 eV corresponds to the carbon in the C(0)NH group. See FIG. 8A. Asexpected, the grafted lamellar crystals displayed a significant N(1s)band. See FIG. 8B. The N(1s) peak located at E_(b)=399 eV was attributedto the nitrogen in the —C(O)NH group.

In sum, the above FTIR and XPS characterization demonstrated thatApplicants have covalently attached an organic coupling agent to thehydroxyl groups of the phosphate on the surfaces of α-ZrP crystals.

Thermogravimetric Analysis (TGA)

FIG. 8C shows the thermogravimetric analysis (TGA) of pristine andgrafted crystals. The final product of the thermo-decomposition ofpristine α-ZrP is ZrP₂O₇ [Zr(HPO₄)₂.H₂O(S)+heat (700°C.)→ZrP₂O₇(s)+2H₂O(g)] exhibits a weight loss of about 12%. On the otherhand, grafted crystals presented a weight loss of about 37%. The TGAspectrum showed four regions. The first one ranged from 25° C. to 91°C.; the second one, from 91° C. to 178° C.; the third one, from 178° C.to 505° C.; and the last one, from 505° C. to 800° C. The first regionshows slight loss of solvent from the surface of the crystals. Thesecond region shows evaporation of the water contained between thelayers of the α-ZrP. The third region shows the removal of the aliphaticchains grafted on the surface. Finally, the fourth region showscondensation of the phosphates. The TGA indicated that about 25% ofsample is from the surface modification.

Example 4. Exfoliation of the Modified α-ZrPs

The functionalized crystals were then exfoliated to obtain a mixture ofthin-surface and edge-modified amphiphilic nanosheets. Exfoliated α-ZrPwas obtained by adding tetra-(n-butylammonium) hydroxide (TBA⁺OH⁻,Aldrich, 40% in water) at a molar ratio of ZrP:TBA=1:1 in DI water.During the intercalation reaction, the suspension was subject tosonication (Branson 8510, 40 kHz, Danbury, Conn.) to guarantee theintercalation of the TBA⁺. A complete exfoliation of the crystals mighttake several minutes to hours. A schematic representation of the α-ZrPcrystal exfoliation is depicted in FIG. 3.

Example 5. Use of α-ZrPs in Emulsions

Mineral Oil in Water Emulsions

Applicants' amphiphilic α-ZrP nanosheets have a large aspect ratio(ξ˜400) due to their extremely thin thickness (about 2.8 nm). See AFMtopography images and section analysis in FIGS. 9A-9C. As stated before,Applicants predicted that high-aspect ratio nanosheets would be able tooffer greater stability between liquid films to prevent coalescence.Their large lateral surface area offers strong adsorption energy at theoil-water interface.

Surfactant-free oil-in-water emulsions stabilized with exfoliatedα-ZrP-ODI containing a mixture of surface- and edge-modified amphiphilicnanosheets were prepared at room temperature. The preparation consistedof adding 700 μL of the exfoliated nano-plate suspension (0.05 g/mL)within 2 mL of H₂O and 300 μL of light mineral oil (Sigma Aldrich). Themixture was treated by sonication for 10 minutes to allow theamphiphilic nanosheets move to the oil-water interface. Dye was added tothe oil phase to make the oil fluorescent for confocal microscopyobservation. Optical and confocal micrographs of the oil-in-wateremulsions are shown in FIGS. 10A and 10B, respectively.

A control emulsion was prepared using the same procedure with anexfoliated non-modified α-ZrP suspension. FIGS. 10C and 10F illustratethe oil-water (o/w) emulsion comparison between the use of non-modifiedand modified α-ZrP as surface-active agents, respectively. The emulsionof the former lasted only for a couple hours, while the latter lastedfor months. An optical microscope was used to observe in detail the o/wemulsions.

FIGS. 10D and 10G show the emulsions for both cases when freshly madejust after sonication. In the case of FIG. 10G, it should be noted thatunder white light, the α-ZrP-ODI nanosheets are difficult to observe dueto their extreme thin thickness. After 24 days, optical micrographs wereobtained for the emulsions. In comparison with FIG. 10D, the controlemulsion optical micrograph (FIG. 10E) elucidates coalescence of the oildroplets. The micrographs for the emulsion stabilized using exfoliatedα-ZrP-ODI can be found at FIG. 10H (top of the emulsion) and FIG. 10I(middle), where no significant coalescence was observed. In contrast toFIG. 10I, no emulsion droplets were found at the 24th day in the middleof the sample shown in FIG. 10C due to the coalescence and creaming inthe emulsions made using non-modified α-ZrP nanosheets.

Stabilization of Aromatic Liquids in Water Emulsions

To study the capability of the α-ZrP-ODI nanosheets to emulsifyimmiscible aromatic liquids, emulsions of toluene-in-water andstyrene-in-water were evaluated. For the toluene-in-water emulsions, thedroplet size dependence was studied by increasing the amphiphilicnanosheet concentration as Binks et al. did using laponite clay. Ashby,N. P.; Binks, B. P. Phys. Chem. Chem. Phys. 2000, 2, 5640.

FIG. 11A displays the toluene droplet diameters for samples withdifferent amounts of α-ZrP-ODI nanosheets. The droplet diameterdecreased with an increase in α-ZrP-ODI nanosheets in a range between0.2 wt. % to 0.62 wt. %. The droplet diameter became constant at a fixedoil concentration (ϕ_(o)=0.085). In general, an increase in amphiphilicnanosheets results in a decrease in toluene droplet size. Also, thetoluene-in-water emulsion droplet diameter and the emulsion stabilitywere studied by varying the oil content. FIG. 11B displays the toluenedroplet diameters for six samples with varied toluene volume fractionsfor a fixed α-ZrP-ODI nanosheet concentration (0.45 wt. %) over a periodof a week. The toluene-in-water emulsion stability was measured for thesix samples. All emulsions were stabilized after 100 h. It was foundthat droplet diameter increased with oil content. See FIG. 11B.

In this experiment, a small size distribution for the droplets wasdetected, similar to previous Pickering emulsion observations (FIG.12A). Simply by changing the nanosheet system from α-ZrP-ODI tonon-modified α-ZrP nanosheets, we obtained droplets from monodispersedto polydispersed, as shown in FIGS. 12A-B. Visual observations shown inFIG. 12C revealed that the toluene-in-water emulsion stabilized bynon-modified nanosheets had undergone a much more evident creamingprocess than the emulsion stabilized by α-ZrP-ODI nano sheets.

In addition, microscopic images were taken to visually inspect thetoluene-in-water emulsions. The image in FIG. 12A illustrates that thetoluene droplets are highly uniform. A microscopic image oftoluene-in-water emulsions, stabilized by non-modified α-ZrP monolayersas a surfactant, is displayed in FIG. 6B. The image in FIG. 6B had thesame composition and had settled for the same amount of time as thesamples with α-ZrP-ODI nanosheets in FIG. 6A. Also, in FIG. 6C, creamingis more evident in the toluene-in-water emulsions stabilized by α-ZrPnanosheets (right) compared to that stabilized by α-ZrP-ODI nanosheets(left).

Example 6. Pickering Miniemulsion Polymerization

The stable Pickering emulsions that Applicants observed aboveestablished the viability of producing a Pickering miniemulsionpolymerization of styrene using α-ZrP-ODI nanosheets as stabilizers,generating armored latex particles similar to the armored latexsuspensions of Bon and Colver. Bon, S. A. F.; Colver, P. J. Langmuir2007, 23, 8316. Applicants performed six Pickering miniemulsionpolymerizations of styrene by varying the quantity of α-ZrP-ODInanosheets from 0.22 to 1.32 wt. % in aqueous solutions at a constantmonomer volume fraction of styrene, approximately ϕ_(o)=0.085.Azobisisobutyronitrile (AIBN, Sigma Aldrich) was used as an initiatorfor the polymerization. Stable Pickering miniemulsions of submicronα-ZrP-ODI colloidosomes were generated via sonication and weresubsequently polymerized at 65° C. for two days. It was observed thatpolystyrene particle diameter was decreased by increasing theamphiphilic nanosheet content. See FIG. 13.

FIG. 14A shows an SEM image after polymerization of styrene in aPickering miniemulsion using α-ZrP-ODI nanosheets as stabilizers. Theimage confirms the formation of polystyrene-α-ZrP-ODI-nanosheetsparticles with a size 215±52 nm. In addition, TEM images were also takenof the platelet-armored polystyrene particles. See FIGS. 14B-D. FIGS.8B-C show that styrene emulsions were able to form non-sphericalparticles showing facet edges and non-smooth corners due to the locationof the α-ZrP-ODI nanosheets at the styrene-water interface. Also, as inthe case of optical microscopy for mineral oil-in-water andtoluene-in-water, observation of the α-ZrP-ODI nanosheets in SEMmicrographs is difficult due to their atomic thickness and because thenanosheets were fused on the polystyrene surface. From the TEMmicrograph (FIG. 8D), the α-ZrP-ODI nanosheets constituted a layer about2-nm thick surrounding the polystyrene core.

Evaluation of Surface Coverage

Since styrene emulsification utilized the strong adsorption propertiesof the nanosheets at the styrene-water interface, the adsorption processwas analyzed in a similar way as Bon et al. Bon, S. A. F.; Colver, P. J.Langmuir 2007, 23, 8316. Calculations were made to determine the amountof platelets on the polystyrene particle surface and the amount ofamphiphilic platelets remaining in the continuous phase. The excessconcentration was calculated from the following equation:C_(surface)=3π/2 ρ_(ZrP-ODI) (_(nanosheets)/ρ_(polystyrene))(h/d_(polystyrene)) C_(polystyrene), where h is the thickness of thenanosheets, C_(surface) (gg⁻¹) is the concentration of amphiphilicnanosheets in the continuous phase, and C_(o) (gg⁻¹) is the totalconcentration of the amphiphilic nanosheets. pZrP-0DI_(nanosheets) andρ_(polystyrene) are the densities of the ZrP-ODI nanosheets and thepolystyrene, respectively. The values of d_(polystyrene), the averagediameter of the polystyrene particle suspensions was obtained from FIG.13. The average diameter of each sample was applied to the equationabove to find the surface concentration of α-ZrP-ODI nanosheets. FIG. 15displays a plot of the α-ZrP-ODI nanosheets on the surface versus thetotal concentration of α-ZrP-ODI nanosheets. The line of best fit has anR² value of 0.99, which proves a strong linear relationship. From thisrelationship, it is demonstrated that the partition, I′ of theamphiphilic nanosheets on the surface versus in the continuous phase wasa constant. By adding more α-ZrP-ODI nanosheets in the emulsions,therefore, surface areas created by these nanosheets producedsmaller-sized emulsions (FIG. 13) due to their high surface activity.For a fixed amount of styrene, therefore, the final particle diameterwas set by the quantity of amphiphilic nanosheets, M, if the sizepolydispersity of the resulted particles was not high, because theamount of nanosheets on the surface would be M×I′, and only a singlelayer of nanosheet was on the surface. See FIG. 14D.

Example 7. Contact Angle Measurements

Applicants also performed contact angle measurements of the α-ZrP-ODInanosheets suspensions on polydimethylsiloxane (PDMS) films to determinethe surface tension between a hydrophobic surface of PDMS and theamphiphilic nanosheet suspensions. See FIGS. 16A-16D.

A Phantom V4.2 camera (Vision Research, Wayne, N.J.) with ahigh-magnification lens, together with the active contours method formeasuring high-accuracy contact angles using ImageJ was used to measurethe surface tension of the PDMS-water interface. A glass slide wascoated with PDMS to simulate similar surface tension interactions as ina PDMS-in-water suspension. The static contact angles were measured forseven different samples at different α-ZrP-ODI nanosheet concentrations,as shown in FIGS. 16A-16D. Using Young's equation, Y_(sl)=Y_(sa)−Y_(la)cos θ, where Y_(sl), Y_(sa) and Y_(la) correspond to the PDMS-liquid,PDMS-air and liquid-air surface tensions, respectively. The values takenfor Y_(sa) and Y_(la) were 21.8 dyn/cm⁵ and 72.8 dyn/cm⁶, respectively.FIGS. 16A-16D show a similar tendency when compared to FIG. 11A and FIG.13, where α-ZrP-ODI nanosheet concentrations between 0.2 t wt. % and0.62 wt. % caused a decrease in surface tension and polystyrene particlediameter.

As α-ZrP-ODI nanosheet concentrations were reduced from 0.2 wt. % to 0.6wt. %, the surface tension was also reduced. The reduction of thesurface tension was in a good correlation with the emulsion sizereduction in the above experiments of toluene and styreneemulsification. Without being bound by theory, this correlation mightindicate that the α-ZrP-ODI nanosheets would reduce the oil-waterinterfacial tension, enabling them to create new surfaces. Without againbeing bound by theory, the underlying mechanism could be the highflexibility of α-ZrP-ODI nanosheets. See FIGS. 4A-4D. The nanosheets cancurve on to the surface of the oil droplets and make small emulsiondroplets. In the case of Gemini nanosheets, the hydrophobic tails canstick into (for the one on the oil side) or bend toward (for the ones onthe other side, as the length of the ODI is about 2 nm) the oil phase.

Example 8. Production of Monolayer Films

Monolayer films of the desired alkylsilanes (APTES or OTS) were firstprepared on cleaned and oxidized Si(100). Next, ZrP nano-plates (ornanosheets) were deposited through self-assembly using a suspension ofthe ZrP nanosheets (nanosheets) in a suitable solvent (EtOH for APTESand toluene for OTS). Si(100) substrates were cleaned and hydroxylatedwith a basic piranha solution (4:1:1 (v:v:v) mixture of high purityH₂O:H₂O₂(30%):NH₄OH) at 80° C. for 30 minutes. The substrates wererinsed under high-purity water for 60 seconds, then with ethanol, andfinally dried under streaming nitrogen. Then the substrate was incubatedin 1 wt. % solutions of desired alkylsilanes (APTES or OTS) in asuitable solvent (EtOH for APTES and toluene for OTS) for ca. 15 hours.The modified substrates were rinsed under high-purity water for 60seconds, then with ethanol, and finally dried under streaming nitrogen.Finally, the ZrP nano-plates (or nanosheets) were deposited throughself-assembly using a suspension of the ZrP nanosheets in a suitablesolvent (EtOH for APTES and toluene for OTS) for 5 hours. The finalobtained substrate were rinsed under high-purity water for 60 seconds,then EtOH, and finally dried under streaming nitrogen. See FIGS. 9A-9C.

Effect of the Amphiphilic Nano-Sheet Chain Length and Configuration inO/W Emulsions

Example 9. Carbon Chain Length (C18, C14, C8, and C5)

Octadecyl isocyanate, tetradecyl isocyanate, octyl isocyanate and pentylisocyanate compounds were successfully grafted on the surface of ZrP(FIG. 17). Subsequently, Janus and Gemini nano-sheets were obtained fromexfoliation of the surface-modified compounds.

To determine the effect of the coupling agent configuration chainlength, oil in water emulsions were fabricated using the ZrP-ODInano-sheets. In this experiment, a WOR (water-to-oil) ratio of 9 wasset, dodecane was used as the dispersed phase, and the sonication powerwas set for 8 Watts for 30 seconds. The nano-sheet surfactantconcentration was varied in a range between 0.04 and 4 wt. %.

Emulsion size as a function of nano-sheet surfactant concentration wasanalyzed. The emulsions were stabilized using nano-sheet surfactanthaving a hydrocarbon chain length of C18, C14, C8, and C5. Fromexperimental data, it was observed that oil-in-water emulsionsstabilized by nano-sheets modified with octyl isocyanate (C8) and pentylisocyanate (C5) presented a plateau region in a concentrations largerthan 0.05 wt. %, whereas oil-in-water emulsions stabilized usingoctadecyl isocyanate (C18) and tetradecyl isocyanate (C14) nano-sheetsonly reached the plateau region at concentrations larger than 1 wt. %.

Based on the emulsion size, the oil-in-water emulsions stabilized by C14and C8 nano-sheet surfactants produced smaller emulsion sizes comparedto C18 and C5. Oil-in-water emulsions stabilized by C14 and C8nano-sheets resulted in an emulsion size of around 310 nm in the plateauregion. However, at the plateau region, emulsions stabilized by C14nano-sheets presented lower emulsion sizes compared to C18, C8 and C5.Macroscopic observations of the nano-sheet surfactant stabilizedemulsions were also analyzed.

In summary, highly stable oil-in-water emulsions were obtained atvarying grafted hydrocarbon chain lengths on the ZrP surfaces. Based onpreliminary data, a chain length of C14 and C8 seems to be moreefficient compared to C18 and C5. This behavior can be explained from tothe competition of the nano-sheet surfactants to aggregate and attach tothe liquid-liquid interface. Large hydrocarbon chain lengths (C18) mayinduce nano-sheet self-assembly, whereas lower hydrocarbon chain length(C5) grafted on the nano-sheets are able to stabilize emulsions andprevent particle aggregation. Oil-in-water emulsions stabilized by C14nano-sheets presented lower emulsion sizes compared to the other three.

Example 10. Chain Configuration (Linear vs. Branched)

Chain configuration effect on oil-in-water emulsion size was evaluated(FIG. 18). The surface of ZrP was grafted using linear and branchedhydrocarbons chains. N-Butyl isocyanate was the linear hydrocarboncompound, whereas sec-butyl isocyanate and tert-butyl isocyanate werethe branched compounds. n-butyl isocyanate, s-butyl isocyanate, andt-butyl isocyanate were successfully grafted. Subsequently, Janus andGemini nano-sheets were obtained from exfoliation of thesurface-modified compounds.

To determine the effect of a coupling agent configuration chain,oil-in-water emulsions were fabricated using ZrP-ODI nano-sheets. Inthis experiment, a WOR (water-to-oil) ratio of 9 was set, dodecane wasused as the dispersed phase, and sonication power was set for 8 Wattsfor 30 seconds. The nano-sheet surfactant concentration was varied in arange between 0.04 and 4 wt. %.

Oil-in-water emulsion size as a function of nano-sheet surfactantconcentration for different chain configurations was analyzed. Theemulsions were stabilized using nano-sheet surfactant having ahydrocarbon chain configuration of n-C4, s-C4, and t-C4. In general,from the experimental data, it was observed that the oil-in-wateremulsions stabilized by nano-sheets modified with n-butyl, s-butyl, andt-butyl isocyanate presented a plateau region at a concentration above0.5 wt. %. Very interestingly, it was found that at a concentration of0.04 wt. %, the emulsions stabilized by the n-butyl isocyanate presenteda significantly lower droplet size compared to the other two chainconfigurations. This observation may confirm the prediction that linearchains are better emulsion stabilizers since linear chains can present abetter arrangement of the hydrophobic molecules on the oil-waterinterface.

In summary, highly stable oil-in-water emulsions were obtained atvarying grafted hydrocarbon chain configuration on the ZrP surfaces.Preliminary data showed oil-in-water emulsions stabilized by then-C4-nano-sheets presented a lower droplet size compared to s-C4 andt-C4 at low nano-sheet surfactant concentration. However, at the plateauregion (>0.5 wt. %), the oil droplet size became the same for the threechain configurations.

Example 11. Amide Group

It is believed that the polymerization is a normal free radicalpolymerization procedure due to the type of peroxide initiators employedand the reaction was very fast at the beginning, starting from the pointwhen free radicals were produced. A comparison of FTIR spectra fornon-grafted ZrP and PNIPAM-grafted ZrP (ZrP-PNIPAM) was performed. The³¹P{¹H} and CP ³¹P{¹H} MAS NMR spectra were recorded at a spinning rateof 10 kHz in a sample of ZrP-PNIPAM. Subtraction of the CP ³¹P{¹H}spectrum from the ³¹P{¹H} spectrum was performed. The CP ¹³C {¹H} MASNMR spectrum were recorded at spinning rate of 10 kHz. The presence ofnew and characteristic bands for the attachment of PNIPAM chains wasobserved and were assigned as follows: 3254 cm⁻¹ (secondary amide N—Hstretching), 2864 to 2964 cm⁻¹ (—CH3 asymmetric and symmetricstretching), 1629 cm⁻¹ (secondary amide C═O stretching), and 1533 cm⁻¹(secondary amide N—H bending).

The attachment of PNIPAM chains on the surface of ZrP were alsoconfirmed via CP-MAS (Cross Polarization Magic Angle Spinning) SolidState NMR experiments. The ³¹P{¹H}, CP ³¹P{¹H} and CP ¹³C{¹H} MAS NMRexperiments were performed with a Bruker Avance-400 spectrometer (400MHz for ¹H nuclei) using a standard 4-mm MAS probe head at a spinningrate of 10 kHz. Standard one pulse (direct nuclear excitation) and/or CPpulse sequences were applied in these experiments at the contact timesof 2 (¹³C nuclei) and 6 (³¹P nuclei) milliseconds. The externalstandards used for ¹³C and ³¹P NMR experiments were tetramethylsilane(TMS) and H₃PO₄ solution, respectively.

The CP ³¹P{¹H} MAS NMR spectrum of the compound showed two resonances at18.8 and 20.5 ppm. The most intense signal was at 20.5 ppm and can beassigned to the orthophosphate group of ZrP. The orthophosphate groupconsists of a phosphorus atom bonded to three Zr atoms through threeoxygen atoms. The weak resonance at 18.8 ppm is also characteristic ofZrP. There were no dramatic changes ongoing from CP to the spectrumobtained by direct excitation (see the ³¹P{¹H} MAS NMR spectrum). Only anon-intense shoulder appeared at −22/−23 ppm. This shoulder was betterseen by subtraction of the CP ³¹P{¹H} spectrum from the ³¹P{¹H}spectrum. Typically, the non-intense shoulder could be assigned to thedehydrated phase of ZrP and/or to a —P—O—C— linkage in a modified ZrPsurface. Given that the sample was polymerized in water (≤50° C.) anddried at 70° C., it can be safely assumed that this signal should belongto the —P—O—C— linkage in a modified ZrP surface and confirms theattachment of the polymer chains.

The ¹³C CP MAS NMR spectrum showed resonances at 174.8, 41.1, 34.1, and22.2 ppm, corresponding to polymer units. According to the layerednature of the material and low coverage, peaks showing the chemicalbonding between the polymer and ZrP were weak (interpretation of ³¹P{¹H}MAS NMR), thus the corresponding ¹³C NMR peaks may be masked by theintense peak at 41.1 ppm. Nevertheless, the presence of the other peaksqualitatively confirms the presence of polymer units.

Example 12. Polyamine Group

As ZrP-PA nano-sheet concentration was increased, a growing trend wasobserved in aqueous foam. Effect of ZrP-PA nano-sheet concentration onfoam stabilization was analyzed: 1) Aqueous foams 7 days afterpreparation as a function of ZrP-PA nano-sheet concentration: thenano-sheet suspension of batch A was used in this experiment at a PA:ZrPmolar ratio of 2.16 0.05, the nano-sheet concentrations were 0.5 0.1, 10.1, 1.5 0.1 and 2 0.1 wt. %; 2) Foam volume as a function of nanosheetconcentration at different times after preparation. A higher nano-sheetconcentration enabled local adsorption of a greater amount of particlesonto the air-water interface. As the nano-sheet concentration increases,more air-water interface can be stabilized. The effect of silica spheresand sodium dodecyl sulfate (SDS) concentration on the amount of aqueousfoams has been reported. For example, it was reported that an increasein particle concentration enhances stability of aqueous foams. Similarresults were obtained using partially hydrophobic silica spheres,crystalline sodium chloride (NaCl) particles modified with cetyltrimethyl-ammonium bromide (CTAB), and modified disk-like particles. Inthe instant Application, it was observed that the amount of aqueousfoams made with ZrP-PA nano-sheets of similar hydrophobicity and wasproportional to the concentration of particles in the bulk. Foamstability was analyzed for each suspension at different times afterpreparation. Interestingly, at equilibrium, foam volume became linearlydependent on the nano-sheet concentration. Hence, the ability tostabilize foam is proportional to the coverage of particles at theinterface. An enhanced surface coverage prevents the diffusion of airmolecules between the bubbles; therefore, as the nano-sheetconcentration increases, so does the stability of aqueous foams.

Example 13. Zirconium Phosphate with Epoxy

To confirm that a peak at 5.0° (17.5 Å) is from restacked exfoliatedR-ZrP nanoplatelets, intercalated and exfoliated R-ZrP samples werecharacterized directly in a liquid state. XRD patterns of R-ZrPintercalated by TBA+OH— at 0° C. in aqueous dispersion were analyzed.Intercalated and exfoliated R-ZrP nanoplatelets were restacked and driedon a silicon wafer before testing. In the liquid state, if the R-ZrP wasexfoliated, the peak at 5.0° should be absent while the peakscorresponding to intercalated R-ZrP (5.8°) and intact R-ZrP (11.7°)should remain. Two selected XRD patterns at intercalation ratios of1:0.30 and 1:0.80 were analyzed. Compared with their dry state XRDpatterns, no diffraction peak at 5.0° position was observed from eitherof the two samples. For the system at an intercalation ratio of 1:0.30,it shows two peaks at 5.8° (15.2 Å) and 11.7° (7.6 Å) in its dried stateXRD pattern. These two peaks were also present in the liquid-state XRDpattern. For the system at an intercalation ratio of 1:0.80, there wasno peak presented in the liquid-state XRD pattern. This result againindicates that the peak at 5.0° (17.5 Å) is from the restackedexfoliated R-ZrP nanoplatelets, while the peak at 5.8° (15.2 Å) is fromthe intercalated R-ZrP nanoplatelets. A large and broad peak at about25.9° was from Mylar film.

XRD patterns of epoxy/R-ZrP nanocomposite containing 0.7 vol % of R-ZrPbefore and after curing were also analyzed. The XRD pattern ofepoxy/R-ZrP nanocomposite before curing showed no peaks, indicating thatR-ZrP nanoplatelets remain exfoliated after mixing with epoxy resin. Inthe case of cured epoxy/R-ZrP nanocomposite, the XRD pattern onlyexhibits a broad hump at around 18° in 2θ, which corresponds to thestructure of the amorphous epoxy matrix.

Example 14. Ester Group

X-ray diffraction pattern of ethyl ester phase is given in Table 2.Thermogravimetric weight-loss curves for Zr(O3POC2H5)2 were prepared forxH2O prepared by (a) ester interchange in 1 mol dm⁻³ ethyl phosphate and(b) direct precipitation. The first weight loss, which occurred below100° C., amounted to 1.45% which is equivalent to the loss of 0.28 molof water. At about 260° C., organic material began to be lost, followedby an abrupt change in slope at about 370° C., signaling the end of thisprocess. The final weight loss, which occurred above 370° C., wasaccounted for by the loss of 1 mol of water resulting from thecondensation of hydrogenphosphate groups.

TABLE 2 X-Ray diffraction patterns of Zr(O3POR)2- type x-zirconiumphosphate esters. R═C₂H₅ (CH₂)₃CH₃ CH₂CHOHCO₂H d/Å I/I_(o) d/Å I/I_(o)d/Å I/I_(o) 11.9 100 15.8 100 14.3 100 5.94 5 7.9 25 7.15 20 4.48 355.21 5 4.73 7 3.87 45 4.4 20 4.36 20 3.19 10 3.97 50 3.84 10 2.67 133.46 15 3.34 5 2.61 10 2.97 8 3.29 5 2.66 10 2.64 10 2.62 10

Example 15. Carbonyl, Aryl Group (J. Chem. Soc., Dalton Trans., 2002,2937-2947)

Solid state MAS NMR spectrum of acetone-2-¹³C sorbed on pillaredsulfonated zirconium biphenylenebis(sulfophosphonate) in which thesurface is saturated by acetone at room temperature at a level of 0.47mmol per gram was analyzed. Resonance at 243 ppm was identified andrepresents the protonated acetone species and the minor peaks are thesame for polymerized acetone derivatives. Starred peaks representedspinning side bands.

Example 16. Silane Group

FTIR of pristine α-ZrP and α-ZrP modified with octadecyltrichlorosilane(OTS), octadecylphosphonic acid (ODPA), 1,2-epoxyoctadecane (EOD), andoctadecylisocyanate (ODI) was analyzed. Relative transmittance (%) as afunction of wavenumbers (cm⁻¹) were determined. TGA of pristine α-ZrPand α-ZrP modified with octadecyltrichlorosilane (OTS),octadecylphosphonic acid (ODPA), 1,2-epoxyoctadecane (EOD), andoctadecylisocyanate (ODI) was also analyzed.

Example 17. Epoxy Group

X-ray diffraction powder patterns of (a) R-ZrP/epoxy, (b) neat/epoxy,and (c) M-R-ZrP/epoxy were prepared. The X-ray diffraction powderpattern of the M-R-ZrP/epoxy nanocomposite showed broad humps around 2°,10°, and 20° in 2θ, which is different from M-R-ZrP. The powder patternexhibited the amorphous nature of the nanocomposite material. The firsttwo humps can be assigned to the inorganic matrix, while the third largebroad hump was assigned to the epoxy matrix. In the case of R-ZrP/epoxy,the powder pattern showed a peak at 7.34 Å; this value was 7.58 Å in thestarting R-ZrP. This change in the interlayer spacing is probably due tothe loss of the water molecule, induced by heating during thepolymerization process, and showed that the layer structure has not beendisturbed by the epoxy.

To directly investigate the dispersion and the state ofintercalation/exfoliation of R-ZrP in the epoxy matrix, OM, SEM, and TEMobservations were performed. The SEM images of R-ZrP powder beforeintercalation showed aggregated primary particles having sizes insubmicrometer range. After intercalation R-ZrP particles with themonoamine and dispersion in epoxy, the nanocomposite panel becametransparent with a slight yellowish color induced by surface oxidation,which is commonly found in cured epoxies. The M-R-ZrP/epoxy panel showedno visible aggregation. In comparison, the composite R-ZrP/epoxy wasopaque and dark-brown in color, indicating the existence ofsubmicrometer size R-ZrP aggregates.

In summary, in the aforementioned Examples, Applicants have demonstratedthe fabrication of thin amphiphilic nanosheets by exfoliating α-ZrPcrystals grafted with a coupling agent of hydrophobic molecules on theiredges and outer surfaces. Their chemical structures were confirmed viaXPS, TGA, and FTIR measurements. Octadecyl isocyanate is a powerfulfunctionalization agent to initiate the surface reaction of α-ZrP.Applicants anticipate that this functional group opens doors for furtherfunctionalization of α-ZrP to diversify applications. These novel thinamphiphilic nanosheets were used to stabilize surfactant-freeoil-in-water emulsions. TEM revealed that there was only a single layerof nanosheets on the interface. Stable uniform toluene-in-wateremulsions were observed by using the amphiphilic nanosheets asstabilizers. In contrast, controlled experiments using the non-modifiednanosheets produced highly polydispersed emulsions. It confirmed thatα-ZrP-ODI nanosheets were attracted to the oil-in-water interface. Thepolymerization of Pickering miniemulsions to produce polystyreneparticles were performed similarly to the method of Bon et al. Bon, S.A. F.; Colver, P. J. Langmuir 2007, 23, 8316. From the emulsion sizemeasurements, it was found that the partition I′ of the amphiphilicnanosheets on the surface was constant, and by adding more α-ZrP-ODInanosheets to the emulsions, surface areas were created by thesenanosheets, producing smaller sized emulsions. Applicants also confirmedthat the α-ZrP-ODI nanosheets might be able to reduce the oil-in-watersurface tension by using nanosheets.

Without further elaboration, it is believed that one skilled in the artcan, using the description herein, utilize the present invention to itsfullest extent. The embodiments described herein are to be construed asillustrative and not as constraining the remainder of the disclosure inany way whatsoever. While the preferred embodiments have been shown anddescribed, many variations and modifications thereof can be made by oneskilled in the art without departing from the spirit and teachings ofthe invention. Accordingly, the scope of protection is not limited bythe description set out above, but is only limited by the claims,including all equivalents of the subject matter of the claims. Thedisclosures of all patents, patent applications and publications citedherein are hereby incorporated herein by reference, to the extent thatthey provide procedural or other details consistent with andsupplementary to those set forth herein.

The invention claimed is:
 1. An amphiphilic nanosheet comprising:lamellar crystals; a plurality of functional groups appended to thelamellar crystals; and wherein the lamellar crystals are stacked intolayered compounds and exfoliated into layers; wherein the plurality offunctional groups comprises one or more of an alkyl group, an arylgroup, an amine group, an amide group, an ester group, an epoxy group, acarbonyl group, an alcohol group, urethane, isocyanate, and aminosilane;wherein the nanosheet comprises at least two regions, a first region anda second region, wherein the first region is hydrophilic, and whereinthe second region is hydrophobic, and wherein the nanosheet comprises aC14 hydrocarbon chain and a C8 hydrocarbon chain that are grafted to thelamellar crystal.
 2. The amphiphilic nanosheet of claim 1, wherein thelamellar crystals are selected from the group consisting of clays,zirconium phosphates, titanium phosphates, hafnium phosphates, siliconphosphates, germanium phosphates, tin (IV) phosphates, lead (IV)phosphates, niobates, titanates, organic crystals, graphites, graphenes,polyhydroxybutyric acids, and combinations thereof.
 3. The amphiphilicnanosheet of claim 1, wherein the first region and the second regioncomprise one of a surface, an edge, or a combination of a surface and anedge.
 4. The amphiphilic nanosheet of claim 1, wherein the nanosheet hasa thickness ranging from about 0.5 nm to about 5 nm.
 5. The amphiphilicnano sheet of claim 1, wherein the nano sheet has a diameter rangingfrom about 10 nm to about 10 μm.
 6. The amphiphilic nanosheet of claim1, wherein at least one region of the lamellar crystals isfunctionalized with hydrophobic functional groups and at least oneregion of the lamellar crystals is unfunctionalized or functionalizedwith hydrophilic functional groups.
 7. The amphiphilic nanosheet ofclaim 1, wherein the functional groups are appended to at least oneregion of the lamellar crystals.
 8. The amphiphilic nanosheet of claim1, wherein the nanosheet is capable of self-assembly.
 9. The amphiphilicnanosheet of claim 1, further comprising n-butyl isocyanate that isgrafted to the lamellar crystal.